The present invention relates to a thin film magnetic head which can be used in a magnetic disk drive, and more particularly, relates to a thin film magnetic head having a narrow track width suitable for high density recording.
In recent years, with an improvement of recording density of the magnetic disk drive, it has been keenly required to develop a thin film magnetic head which has excellent read/write characteristics, and to improve performance of a recording medium. At present, a head employing a GMR (Giant Magnetoresistive Effect) element capable of obtaining high read outputs is used as a read head. Moreover, a TMR (Tunneling Magnetoresistive) element and a CPP (Current Perpendicular to Planer) element capable of obtaining much higher read-back sensitivity have also been developed. On the other hand, the conventional inductive thin film recording head making use of electromagnetic induction has been used as a recording head, and a thin film magnetic head having the above described read head and recording head integrally formed has been used.
In order to realize the high density recording, it is necessary to enhance track density as well as linear recording density. In the conventional thin film magnetic head, an effective recording track width in which magnetization of signals is recorded is smaller than an erase width for erasing recorded signals, and there exists an erase band ΔE having a certain width (=erase width−effective recording track width)/2. In the conventional thin film magnetic head, it was difficult to reduce the erase band ΔE. There was such a problem that in the case where the erase width is narrowed by reducing a geometric track width of the recording head, the effective recording track width is also decreased, which may cause deterioration of S/N ratio and overwrite characteristic (O/W).
Further, as the track density is improved and a track pitch is narrowed, a magnetic field generated from the recording head is extended to an adjacent track. As a result, there may be such a problem that a so-called ATI (Adjacent Track Interference) may occur. Measures for solving this problem have been also sought.
Patent Document 1 (Japanese Patent Laid-Open No. Hei 11-306513) discloses a composite type magnetic head, having a structure suitable for high density recording. In this composite type magnetic head, sizes of an upper magnetic pole piece and a lower magnetic pole piece which constitute a write gap are made shorter at a leading side and longer at a trailing side, in a direction of a track width at a side of the write gap, as seen from a face opposed to a medium, and the saturation magnetic flux density of materials for the upper magnetic pole piece is made larger than the saturation magnetic flux density of the lower magnetic pole piece, to thereby decrease a bend and an erase width at a track end of magnetization transition, and to narrow the recording track width.
Patent Document 2 (Japanese Patent Laid-Open No. 2003-36506) discloses a thin film magnetic head in which a front end portion of the lower magnetic pole piece is provided on a main layer of the lower magnetic pole piece, and the front end portion of the lower magnetic pole piece is provided with a protruding step having a larger width than a width of a front end layer of the upper magnetic pole piece, to thereby decrease an unnecessary magnetic field at an off track position.